The objective of this study is to identify a subset of patients with the syndrome of autism in whom genetic and/or congenital factors are etiologically significant and to develop guidelines for genetic counseling. To reach this objective the following specific aims were initially established: 1. To identify a population of families with multiple incidences of autism. 2. To analyze family pedigrees for modes of inheritance. 3. To obtain (a) HLA, (b) chromosomes, and (c) gene marker studies. 4. To compare multiple and single incidence cases and to correlate clinical and biomedical factors. 5. To test hypotheses of viral etiology in autism. The following new aims are established for this renewal application: 6. To identify fragile X chromosomes in multiple incidence families. 7. To identify extended pedigrees with multiple incidences of autism by utilizing the Utah Resource for Genetic and Epidemiologic Research. 8. To identify linkage between autism and specific DNA polymorphisms by utilizing recombinant DNA probes (contigent). Results to date indicate (a) there is an autosomal recessive type of autism, (b) increased HLA antigen sharing between parents of autistics, and (c) a possible linkage between autism and markers on chromosome 9. Hopefully, we shall be able to identify the specific genetic defect on a molecular level and be able to develop a rational basis for treatment and genetic counseling, thus having a positive impact on the health care needs of the nation. These results will be used by clinical geneticists, obstetricians, pediatricians, neurologists, child psychiatrists, and public health specialists.